The present invention relates to a digital color converting apparatus for converting a color by transforming a color image into a digital electric signal and processing the digital image signal. More particularly, the present invention is concerned with a digital color converting apparatus applicable to a digital color copier, a color image processor and others and capable of converting only a particular color of a color image into a desired color.
With a digital color copier, it is often desired to change the color of a part of an image which is carried on an original color document in the event of copying the document. Heretofore, a procedure for reproducing an image which is different in color from an original image as stated has been implemented with an expensive graphic work station. Specifically, the work station reads an original document through an image scanner, writes the resulting image data in an image memory having a large capacity, and displays the entire or a part of the image memory on a cathode-ray tube. Then, the operator marks a particular desired region of the image appearing on the cathode-ray tube by using a cursor and, then, enters a desired alternative color. An image processor changes those data which lie in the marked region into another color as specified by the operator, so that the alternative data are displayed on the cathode-ray tube. After repeatedly specifying the region and color as mentioned, the operator applies the modified image data to a color plotter or the like to produce a copy. A drawback with such an implementation is that the operator has to endure the troublesome and time-consuming work and, in addition, the processor is expensive due to the need for a large capacity image memory and a high resolution color cathode-ray tube.
In relation to an analog color copier, there has been proposed a system for producing a copy in different colors from an original document by changing the combination of color separating filters as well as the combination of colors of toner, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 52-55542. Such a system, however, suffers from a shortcoming that the combination of optical filters cannot be changed without resorting to a complicated mechanism and, moreover, a copying cycle has to be repeated a great number of times to produce a single copy at the sacrifice of time.